1. Field of the Invention
The present invention relates generally to production of an enzyme for use in production of a sweetener. More particularly, the present invention relates to production of arabinose isomerase and tagatose.
2. Description of the Related Art
In recent years, growing concerns about health have led much research effort to the development of healthful foods. As one of the above efforts, sugar alcohols have been proposed as sweeteners which can substitute sugar, known to cause adult diseases, and are practically being used. Since the said sweeteners are known to have adverse side effects such as causing diarrhea when ingested more than certain amount, there is an urgent need to develop substitutional sweeteners without harmful effects.
Among substitutional sweeteners which have little side effect, tagatose, a keto-sugar of galactose, has similar sweetness to D-fructose, and has known not to be absorbed or metabolized in the body, making tagatose a safe low-caloric substitutional sweetener for sugar. Also, it has been reported that tagatose can be employed as an intermediate for the preparation of useful optically active isomers, detergents and cosmetics, also, as an additive or raw material for the synthesis of drugs, especially, its ability to lower blood sugar level renders tagatose a therapeutic and preventive agent for diabetes, and a low caloric diet agent.
Currently, tagatose is mostly prepared via chemical synthesis from galactose (see: U.S. Pat. No. 5,002,612), which comprises the steps of isomerization of galactose catalyzed by metal hydroxide in the presence of inorganic salts to form an intermediate of metal hydroxide-tagatose complex, and neutralization of the complex by adding acid to yield final product, tagatose.
Alternative method for manufacturing tagatose is an enzymatic method in which galactose is converted into tagatose via conversion of aldose or aldose derivatives into ketose or ketose derivatives. Especially, it has been reported that arabinose isomerase which catalyzes the conversion reaction of L-arabinose into L-ribulose can be employed for production of tagatose in vitro using galactose as a substrate. However, the yield of tagatose produced by arabinose isomerase from galactose is as low as 20%, hindering industrial application of conversion process of galactose into tagarose. Although the method for manufacturing tagatose from milk or cheese has been developed (see: U.S. Pat. No. 6,057,135), again, low yield is the limitation for its industrial use.
Under the circumstances, there are strong reasons for exploring and developing a novel enzyme which can produce tagatose with high yield.